1. Field of the Invention
This invention relates to a ceramic honeycomb structural body used as a catalyst carrier for purification of an exhaust gas expelled from an internal combustion engine for automobiles, a diesel particulate filter (hereinafter referred to as DPF), or a catalyst carrier for purification and/or deodorization of an exhaust gas using various gases or petroleum as a fuel and a method of producing the same.
2. Related Art Statement
Recently, catalyst convertors have been used for the purification of exhaust gas from an internal combustion engine in connection with the prevention of air pollution. In general, the catalyst convertor is manufactured by coating a honeycomb structural carrier of cordierite ceramic with an active substance having a large specific surface area such as .gamma.-alumina and carrying a noble metal catalyst such as platinum, palladium, rhodium, or the like, on the .gamma.-alumina layer to form a honeycomb structural catalyst carrier, airtightly inserting this carrier into a casing made from stainless steel or the like through a sealing member, and arranging the casing and carrier in a passage of an exhaust gas discharged from an internal combustion engine, wherein hydrocarbons, carbon monoxide, nitrogen oxide and the like included in the exhaust gas are reduced and purified on the catalyst bed of the honeycomb structural carrier.
Such a ceramic honeycomb structural carrier is manufactured through extrusion molding, drying and firing steps, but inevitable size errors and deformations occur in the ceramic honeycomb structure at each step. Firstly, the extrusion molded product contains water, binder and the like and is very soft at the extrusion molding step, so that it easily deforms by its dead weight. In large products of 300 mm in diameter, for example, if they are extruded in a direction perpendicular to gravity, cells existing in the outer peripheral portion of the product break down by its dead weight, while if they are extruded in a direction parallel to gravity, the lower portion of the product buckles by its dead weight. Secondly, the drying and/or firing of the extrusion molded product can not be carried out completely and uniformly at the drying and firing steps, so that scattering of shrinkage in various portions of a final product results. Therefore, the final product has a drawback that the accuracy of its outer diameter is somewhat poor and also the cylindricity of the final product is poor.